Roberts and manager Buck Showalter won't reveal an exact date that Roberts would report to an affiliate, but they've got a pretty good idea.
"We talk every day," Showalter said. "Probably a little more informed than what Brian is going to talk about publicly. Like I said earlier, it's more a matter of when and not if.
"Hopefully, that's something that's imminent. We've got a plan in place and 99 percent of it is based on what Brian and his doctors are talking about. We're at the point where there's a potential date involved.
"We're just trying to serve his needs and what best fits. It's uncharted territory for people who have dealt with this, and it's a target that's hard to pin down. It's not your normal rehab. You try to stay flexible mentally about it and try not to put deadlines or false things out there - if it's not met.
"On the flip side, things might go better than you perceive, but we're cautious on it just like Brian should be, and we'll continue to support and create the best thing that he and his doctors feel like is for him, which is the best thing for us."
Roberts has been traveling with the team and could make the next trip.
"I wouldn't preclude him going on a trip with us, but a lot depends when this starts and how things are progressing," Showalter said.
Asked if he's considered how he's going to make room for Roberts on the roster, Showalter grinned and replied, "What do you think?"
"Through the years, these things kind of work themselves out," he said. "It's a good problem, but I don't consider it a problem. It's a good adjustment, something we haven't had much. When it happens, and someone is ready to come back, then we'll look at it. I'm more concentrated on the 25 guys and the competition we're facing tonight, trying to stay focused on it.
"To say your mind doesn't sometimes drift to it, I don't think it behooves you to spend much time on it. When the time comes, we'll address it, but you do think about some scenarios. I'm trying to stay focused on how the guys who are here now are playing. Sometimes you find out some things that normally you wouldn't get to find out. It's an opportunity."
Showalter shot down the idea that Roberts could return as a role player, and it's a victory just to have him on the active roster.
"Role player? I don't think of it like that at all," Showalter said.
"I think Brian is looking at it as a lot more than just getting here. Brian wants to get here and bring what Brian can bring, and we all know what that capability is. I think he knows what it takes to perform at this level. He's not going to put himself in a position to come back unless he knows he can bring that. He knows what the needs of a player is to play at the level in our division, so I have complete trust in him that he'll know if it's right."
For the Red Sox:
Mike Aviles SS
Dustin Pedroia 2B
David Ortiz DH
Adrian Gonzalez 1B
Will Middlebrooks 3B
Jarrod Saltalamacchia C
Daniel Nava LF
Marlon Byrd CF
Che-Hsuan Lin RF
Clay Buchholz RHP
One more note: The Diamondbacks have called up third baseman Josh Bell.